Tobacco smoking during pregnancy retards fetal growth as manifested by decreased birth weight. The fetus is dependent upon the placental transfer of amino acids (AA) from maternal to fetal circulation. Several components of tobacco smoke (nicotine, cyanide, carbon monoxide) interfere with placental AA transport. The specific aims include: (1) Determination of complete AA profiles by HPLC in plasma samples from maternal blood, placental tissue, umbilical venous blood and umbilical arterial blood of smoking and non-smoking pregnant women. These studies will be extended to venous plasma samples of two groups of volunteers, (a) non-pregnant women, smokers and non-smokers; (b) men, smokers and non-smokers. (2) Determination of cotinine, a metabolite of nicotine, in the plasma samples and carboxyhemoglobin (COHgb) in blood samples of smokers to assess their smoking habit. (3) Evaluation of kinetic parameters (Km, Vmax) of the human placental AA uptake system in smokers and non-smokers using model substrate, alpha-aminoisobutyric acid. Evaluation of the kinetic parameters (Km, Vmax) of three enzymes, gammaglutamyltranspeptidase (GGTP), phospholipid-N-methyltransferase (PMT), and choline acetyl-transferase (ChA) in human placentas from smokers and non-smokers. GGTP, PMT and ChA are critical enzymes in the gammaglutamyl cycle (GGC), membrane phospholipid methylation and acetylcholine (ACh) synthesis respectively. GGC, PMT and ACh have been postulated to play regulatory roles in the uptake of AA by placenta. (4) Differences in the responsiveness of umbilical and chorionic plate blood vessels of smokers and non-smokers vasoactive agents. (5) Analysis of venous plasma of smokers and non- smokers and umbilical venous and arterial plasmas of placentas of smokers and non-smokers for 5-hydroxytryptamine. (6) Determination of endothelial muscarinic receptors in chorionic plate blood vessels of smokers and non- smokers. ACh released into the placental circulation stimulates endothelial muscarinic receptors and cause vasodilation. These specific aims will provide information on (a) deficits created in the placental transport of AA by maternal smoking and (b) possible AA disorders in adults due to tobacco smoking.